Get the iOS system version number and use [[[Uidevice Currentdevice] systemversion] floatvalue]--"SDK defects" carefully

The most common way to get a system version of IOS is:

[[[Uidevice Currentdevice] systemversion] floatvalue]

But. This floatvalue is not reliable, this is also a bug in the iOS SDK. Look at the performance of the above function on the 8.2 system.

Assuming the code has inferences for if (version >= 8.2), the inference is invalidated.

Therefore, it is more reliable to use a string-control version.

Get the iOS system version number and use [[[Uidevice Currentdevice] systemversion] floatvalue]--"SDK defects" carefully